Fully-redundant frangible separation system

ABSTRACT

A frangible joint for a structure is provided. The structure is provided having a first portion and a second portion with a feature defining a fracture plane disposed therebetween. A first housing is coupled to a first side of the first portion, the first housing having a first slot adjacent the first side and a first wall member adjacent the feature. A second housing is coupled to the second portion the first housing, the second housing having a second slot adjacent the second side and a second wall adjacent the feature opposite the first wall. A first expanding tube assembly is disposed within the first slot. The first expanding tube assembly having a first tube containing a first explosive core. A second expanding tube assembly is disposed within the second slot. The second expanding tube assembly having a second metallic tube containing a second explosive core.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present Application is a non-provisional application of U.S. Provisional Application Ser. No. 61/945,930 filed on Feb. 28, 2014, the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a device that provides for the separation of a structure, and in particular, to a frangible joint providing full redundancy and improved reliability.

BACKGROUND OF THE INVENTION

Frangible joints of various design configurations are common, for example, those comprising a hollow form extrusion. Also, various devices for shock attenuation are also known, for example, those that include a cylindrical flexible structure having one or more viscoelastic members secured to an outer surface of the cylindrical structure. In this known arrangement, the cylindrical structure has machined features to tune stiffness and shock transmissibility therethrough. The cylindrical structure may be used, for example, as a shock isolation mount between a spacecraft and a launch vehicle.

One type of frangible joint uses an explosive cord to separate one portion of the structure (e.g. the spacecraft or payload) from another section (e.g. the launch vehicle). Typically, the separation mechanism contains a single length of explosive cord in the expanding tube assembly (XTA), consisting of the explosive core, elastomeric charge holder and metallic expanding/confinement tube. When separation is desired, the explosive core is detonated causing the confinement tube to expand. This expansion fractures the joint allowing the portions of the structure to separate.

It should be appreciated that it is desirable to provide a redundant separation mechanism to ensure separation of the structures in the event the first explosive core does not fully or partially detonate. Some systems have been proposed that incorporate two lengths of explosive cord in a single XTA. However, it has been found that this concept may create a risk for fratricide (one explosive cord damages the other) or confinement tube rupture in the event that both cores detonate. Confinement tube rupture is undesirable as it creates unnecessary debris.

Other proposed systems have incorporated two XTAs to create two fracture planes, one for each XTA. If both XTAs properly function in this design, the material between the two fracture planes is separated from both portions of the structure, resulting in large pieces of debris between the separated structures.

Accordingly, while existing frangible joints are suitable for their intended purposes the need for improvement remains, particularly in providing a frangible joint that provides improved reliability through a fully redundant separation mechanism while avoiding undesired fratricide and debris.

SUMMARY OF THE INVENTION

According to an embodiment of the invention, a frangible joint is provided. The frangible joint comprising a structure having a first portion and a second portion with a feature defining a fracture plane disposed therebetween. A first housing is coupled to a first side of the first portion, the first housing having a first slot adjacent the first side and a first wall member adjacent the feature. A second housing is coupled to the second portion on a second side opposite the first housing, the second housing having a second slot adjacent the second side and a second wall adjacent the feature opposite the first wall. A first expanding tube assembly is disposed within the first slot, the first expanding tube assembly having a first metallic tube containing a first explosive core disposed within a first elastomer member. A second expanding tube assembly is disposed within the second slot, the second expanding tube assembly having a second metallic tube containing a second explosive core disposed within a second elastomer member.

According to another embodiment of the invention, a frangible joint is provided. The frangible joint comprising a structure having a first portion, an opposing second portion and a notch disposed between the first portion and the second portion, the structure having a first side and an opposing second side, the notch defining a fracture plane. A first housing is coupled to the first portion on the first side, the first housing having a first slot with a first wall on an end adjacent the notch, the first wall having an end in contact with the first side. A second housing is coupled to the second portion on the second side, the second housing having a second slot with a second wall on an end adjacent the notch, the second wall having an end in contact with the second side. A first expanding tube assembly is disposed within the first slot and having a first metallic tube containing a first explosive core disposed within a first elastomer member, the first expanding tube assembly configured to fracture the structure along the fracture plane in response to a detonation of the first explosive core. A second expanding tube assembly is disposed within the second slot and having a second metallic tube containing a second explosive core disposed within a second elastomer member, the second expanding tube assembly configured to fracture the structure along the fracture plane in response to a detonation of the second explosive core.

According to still another embodiment of the invention, a method of separating portions of a structure is provided. The method comprising providing a structure having a first portion and an adjacent second portion with a notch disposed therebetween. A first housing is provided that is coupled to the first portion and having a first slot adjacent the first portion. A second housing is provided that is coupled to the second portion on a side of the structure opposite the first housing, the second housing having a second slot adjacent the second portion. A first expanding tube assembly is provided having a first metallic tube containing a first explosive core disposed within a first elastomeric member. A second expanding tube assembly is provided having a second metallic tube containing a second explosive core disposed within a second elastomeric member. The first explosive core is detonated to expand the first metallic tube. The structure is fractured at the notch in response to the expansion of the first metallic tube.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments of the present invention can be understood with reference to the following drawings. The components are not necessarily to scale. Also, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 is a perspective view of a portion of a structure having a frangible joint in accordance with an embodiment of the invention;

FIG. 2 is a side view of the frangible joint of FIG. 1 along the line 2-2;

FIG. 3 is a view of the frangible joint of FIG. 2 illustrating the deformation that occurs with one of the explosive cords detonated;

FIG. 4 is a side view of the frangible joint of FIG. 3 with the two portions of the structure separated; and

FIGS. 5-7 are perspective views of a rocket having seams between the fairing halves and the sections of the launch vehicle that include a frangible joint of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is more particularly described in the following description and examples that are intended to be illustrative only since numerous modifications and variations therein will be apparent to those skilled in the art. As used in the specification and in the claims, the singular form “a,” “an,” and “the” may include plural referents unless the context clearly dictates otherwise. Also, as used in the specification and in the claims, the term “comprising” may include the embodiments “consisting of” and “consisting essentially of” Furthermore, all ranges disclosed herein are inclusive of the endpoints and are independently combinable.

As used herein, approximating language may be applied to modify any quantitative representation that may vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially,” may not to be limited to the precise value specified, in some cases. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value.

Embodiments of the present invention provide advantages in allowing the separation of structures in a fully redundant arrangement. Embodiments of the present invention provide advantages in allowing the detonation of a first expanding tube assembly (XTA) while reducing the risk of, or eliminating, fratricide of a second XTA. Embodiments of the present invention provide still further advantages in reducing or eliminating the amount of debris generated during the separation of structures.

The foregoing and other features of various disclosed embodiments of the invention will be more readily apparent from the following detailed description and drawings of the illustrative embodiments of the invention wherein like reference numbers refer to similar elements.

Referring to FIGS. 1 and 2, an exemplary frangible joint 20 is shown for separating a first portion 22 from a second portion 24 of a structure 26. The structure 26 may be any structure that is separated into two or more pieces, such as but not limited to a rocket that separates a spacecraft from a launch vehicle for example. It should be appreciated that while some of the illustrated embodiments show and describe the frangible joint as having a cylindrical shape, this is for exemplary purposes and the claimed invention should not be so limited. In other embodiments, the frangible joint 20 may have other shapes, such as straight and curve-linear shapes for example.

A feature, such as notch 36 is disposed between the first portion 22 and the second portion 24. The notch 36 defines a separation or fracture plane 116 (FIG. 3) where the structure 26 fractures to allow the first portion 22 and second portion 24 to separate. In the exemplary embodiment, a notch 36 is formed on both sides of the structure 26. In one embodiment, the notch 36 is V-shaped having a pair of opposing angled walls with a curved fillet surface at the vertex.

The frangible joint 20 includes a first housing 28 fixedly coupled to the first portion 22. The first housing 28 includes a slot 30 with an open side 32 adjacent a side 34 of the first portion 22. As will be discussed in more detail below, the slot 30 is sized to receive an expanding tube assembly (XTA). The slot 30 is first defined by a first wall 38 and a second wall 40. The wall 38 includes an outer surface 42 adjacent to one side of the notch 36. The wall 38 further has an end 44 in contact with the side 34. On one end, the first housing 28 includes a keyway 46 that engages or interlocks with a second housing 48. In the exemplary embodiment, the keyway 46 has a slot 50 having a pair of angled sides. The slot 50 is sized to receive a protrusion 52 on the end of second housing 48. The protrusion 52 has complementary shaped side walls sized to fit within the slot 50. It should be appreciated that the angled walls of the keyway 46 facilitate the coupling of the first housing 28 to the second housing 48. In the exemplary embodiment, the first housing 28 has an end surface 54 that is offset from the surface 42 of wall 38. As will be discussed in more detail below, the keyway 46 provides advantages in supporting the first housing 28 to reduce the amount of lateral deflection of the end 54 when the XTA is detonated. The keyway 46 further allows the first and second portions 22, 24 to freely separate after fracture of the structure 26.

The second housing 48 is fixedly coupled to the second portion 24. The second housing has a body 56 having a first inner surface 58 and a second inner surface 60. In the exemplary embodiment, the surfaces 58, 60 cooperate with the surface 42 to define an open space 62. In one embodiment, the notch 36 may have an open side that is arranged within or contiguous with the open space 62. As will be discussed in more detail below, the open space 62 allows for deflection of the second portion 24 under certain XTA detonation circumstances.

On an opposite side of the second portion 24 from the second housing 48 is a third housing 64. In the exemplary embodiment, the third housing 64 is substantially a mirror image of the first housing 28. The third housing 64 is fixedly coupled to the second portion 24 and includes a slot 66 with an open side 68 adjacent a side 70 of the second portion 24. As will be discussed in more detail below, the slot 66 is sized to receive an expanding tube assembly (XTA). The slot 66 is first defined by a first wall 72 and a second wall 74. The wall 72 includes an outer surface 76 adjacent to one side of the notch 36. The wall 72 further has an end 78 in contact with the side 70.

On one end, the third housing 64 includes a keyway 80 that engages a fourth housing 82. In the exemplary embodiment, the keyway 80 is a protrusion 84 having a pair of angled sides. The protrusion 84 is sized to receive a slot 86 on the end of fourth housing 82. The protrusion 52 and slot 86 have complementary shaped side walls. As discussed above, the angled walls of the keyway 80 facilitate the coupling of the first housing 28 to the second housing 48. In the exemplary embodiment, the third housing 64 has an end surface 88 that is offset from the surface 76 of wall 72. As will be discussed in more detail below, the keyway 80 provides advantages in supporting the third housing 64 to reduce the amount of deflection of the end 88 when the XTA in the slot 66 is detonated. The keyway 80 further allows the first and second portions 22, 24 to freely separate after fracture of the structure 26.

In the exemplary embodiment, the fourth housing 82 is substantially a mirror image of the second housing 48. The fourth housing 82 is fixedly coupled to the first portion 22 opposite the first housing 28. The fourth housing has a body 90 having a first inner surface 92 and a second inner surface 94. In the exemplary embodiment, the surfaces 92, 94 cooperate with the surface 76 to define an open space 96. The notch 36 on the side of fourth housing 82 may also have an open side that is arranged within or contiguous with the open space 96. As will be discussed in more detail below, the open space 62 allows for deflection of the first portion 22 when an XTA is detonated in the slot 30. In one embodiment, the surface 92 includes a chamfer or fillet surface 98 along an inner edge along the side of the first portion 22. The surface 98 provides a relief that reduces the stress on the first portion 22 when it deflects on the loading from the expanded XTA.

In one embodiment, the housings 28, 82 are coupled to each other and the structure 26 by a plurality of fasteners 100. Similarly, the housings 48, 64 are coupled to each other and the structure 26 by fasteners 102.

It should be appreciated that it is desirable to have redundancy in the frangible joint 20. To provide this redundancy, embodiments of the invention provide for two expansion devices disposed within the slots 30, 66, such as an XTA 104, 106. Providing redundancy improves the reliability of the overall system. As will be discussed in more detail below, each XTA 104, 106 include an explosive device that causes the respective XTA 104, 106 to expand and fracture the structure 26. To reduce shock and the potential for debris, it is desired that the fracturing of the structure be accomplished with one XTA. This allows the other XTA to provide a backup in the event the first XTA does not detonate. In one embodiment, each XTA 104, 106 has a detonator arranged at each end (not shown). The detonators may be activated simultaneously causing the detonation to travel from each end. This ensures desired operation even if one of the detonators does not activate or if there is a break in the XTA's explosive core. Thus if the first XTA does not operate or does not operate completely, the second XTA is then actuated to cause separation of the first portion 22 from the second portion 24.

A conventional XTA 104, 106 has a generally oblong configuration with a metallic containment tube 108. Within the tube 108 is an elastomeric charge holder 110 within which is disposed an explosive core 112 or a linear detonation charge. One suitable charge is a mild detonation fuse known as HNS-IIA Mild Detonating Fuse. Such a fuse typically contains a core of 24 grains per linear foot HNS in an aluminum jacket. It should be appreciated that other detonation materials, such as HMX for example, may be used as well. The elastomeric charge holder 110 may be made from an elastomeric material, such as a silicone polymer for example.

Referring now to FIGS. 3-4, upon detonation, the explosive core 112, the containment tube 108 expands in a direction transverse to the length of the XTA 104. As the XTA 104 expands, the tube 108 is constrained by the walls 38, 40 and pressure is applied to section 114 of first portion 22 and the first housing 28. Since the first housing 28 is substantially constrained by keyway 46 on one end and the fastener 100 on the opposite end, the section 114 deflects toward and into the open space 96 causing the structure 26 to fracture along the fracture plane 116. In one embodiment, the fracture plane 116 is defined along a plane passing through the narrowest point between the vertexes of notches 36. In one embodiment, the surfaces 54, 88 are co-planar with the fracture plane 116. It should be appreciate that some deflection of housings 28, 48 may occur, but that the XTA 104 remains contained within the slot 30. This provides advantages in improving the containment of any debris that may result. Further, the containment of the XTA 104 between the slot 30 and the side 34 provides advantages in eliminating the need for a strap or other holding device that is used to ensure that the XTA remains with the first portion 22 and does not become debris.

It should further be appreciated that the arrangement of the separate XTA 106 on the opposite side of the structure 26 and offset along longitudinal axis of the frangible joint 20 substantially shields the XTA 106 from the detonation and shockwave associated with the fracture of the structure 26. This provides advantages in reducing the risk or eliminating the occurrence of fratricide, allowing the frangible joint 20 to have a full redundancy in the event that the XTA 104 does not activate or an incomplete fracture of the structure 26 occurs. Further, this arrangement allows the XTA 106 to fracture the structure 26 at the same fracture plane 116. Once the structure 26 is fractured at the notch 36, the first portion 22 and second portion 24 are free to separate as illustrated in FIG. 4.

Frangible joint systems 20 have been used in many applications, such as in aerospace applications to quickly, efficiently and reliably separate components. In one embodiment, shown in FIGS. 5-7, the frangible joint 20 is coupled to a space launch vehicle 100. In this embodiment, the frangible joint 20 is coupled fairings 102A, 102B along the longitudinal fairing split line joints 104 to allow the jettison (FIG. 6) of the fairings 102A, 102B to deploy a payload 106 (FIG. 7). The frangible joint 20 may further be used in circumferential base joints 108 and interstage joints 110 that allow a lower stage rocket 112, for example, to be separated from an upper stage rocket 114.

In an embodiment, such as that illustrated in FIGS. 5-7, typically the XTA coupled to the portion with the payload 106 is activated first. Since the launch vehicle 112, 114 and fairings 102A, 102B are typically discarded, this provides advantage of discarding the XTA still having an explosive core and avoids having the payload 106 contain an explosive member. It should be appreciated that this is still accomplished where the first XTA does not activate and the activation of the second XTA (coupled to the payload) separates the structure as the second XTA has been detonated and the explosive core no longer exists.

It should be further appreciated that while embodiments herein describe the frangible joint 20 as being coupled to the adjoining components by fasteners such as bolts, this is for exemplary purposes and the claimed invention should not be so limited. In other embodiments, other fastening means may be used, such as but not limited to welding, adhesives and rivets for example.

It should be further appreciated that while embodiments describe the coupling of the frangible joint 20 in reference to fairings and launch vehicles, this is for exemplary purposes and the claimed invention should not be so limited. In other embodiments, the frangible joint 20 is coupled between the payload, such as a satellite for example, and the structure of the spacecraft or the fairing for example. In other embodiments, the frangible joint 20 is coupled between two different payloads arranged within the spacecraft. In other embodiments, the frangible joint 20 may be used between two stages of a rocket. In still other embodiments, the frangible joint 20 may be used to decouple service panels from the spacecraft.

Embodiments of the present invention provide advantages in providing a reliable means for separating parts with reduced shock imparted to the surrounding structures. A fully redundant arrangement is provided where the explosive cords are arranged in separate XTA's that are disposed to reduce the risk or eliminate the potential for damage to the non-activated XTA when the first XTA is activated. This provides advantages in reducing the risk of or eliminating the potential for fratricide (severing the non-activated XTA) or confinement shell rupturing. Embodiments of the present invention provide still further advantages in providing a fully redundant frangible joint with a single fracture plane, further reducing the amount of or eliminating the generation debris.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. All citations referred herein are expressly incorporated herein by reference. 

1. A frangible joint, comprising: a structure having a first portion and a second portion with a feature defining a fracture plane disposed therebetween; a first housing coupled to a first side of the first portion, the first housing having a first slot adjacent the first side and a first wall member adjacent the feature; a second housing coupled to the second portion on a second side opposite the first housing, the second housing having a second slot adjacent the second side and a second wall adjacent the feature opposite the first wall; a first expanding tube assembly disposed within the first slot, the first expanding tube assembly having a first metallic tube containing a first explosive core disposed within a first elastomer member; and a second expanding tube assembly disposed within the second slot, the second expanding tube assembly having a second metallic tube containing a second explosive core disposed within a second elastomer member.
 2. The frangible joint of claim 1 further comprising: a third housing coupled to the second portion opposite the second housing, the third housing defining a first open space directly adjacent the second portion; and a fourth housing coupled to the first position opposite the first housing, the fourth housing defining a second open space directly adjacent the first portion.
 3. The frangible joint of claim 2 wherein the first housing is removably coupled to the third housing adjacent the feature, and the second housing is removably coupled to the fourth housing adjacent the feature.
 4. The frangible joint of claim 3 wherein the first slot has a first open end adjacent the feature, and the second slot has a second open end adjacent the feature and opposite the first open end.
 5. The frangible joint of claim 3 wherein the first housing is coupled to the third housing by a first keyway, and the second housing is coupled to the third housing by a second keyway.
 6. The frangible joint of claim 1 wherein the first slot and the first expanding tube assembly are configured to fracture the structure along the fracture plane when the first explosive core is detonated.
 7. A frangible joint comprising: a structure having a first portion, an opposing second portion and a notch disposed between the first portion and the second portion, the structure having a first side and an opposing second side, the notch defining a fracture plane; a first housing coupled to the first portion on the first side, the first housing having a first slot with a first wall on an end adjacent the notch, the first wall having an end in contact with the first side; a second housing coupled to the second portion on the second side, the second housing having a second slot with a second wall on an end adjacent the notch, the second wall having an end in contact with the second side; a first expanding tube assembly disposed within the first slot and having a first metallic tube containing a first explosive core disposed within a first elastomer member, the first expanding tube assembly configured to fracture the structure along the fracture plane in response to a detonation of the first explosive core; and a second expanding tube assembly disposed within the second slot and having a second metallic tube containing a second explosive core disposed within a second elastomer member, the second expanding tube assembly configured to fracture the structure along the fracture plane in response to a detonation of the second explosive core.
 8. The frangible joint of claim 7 further comprising: a third housing coupled to the second portion on the first side, the third housing defining a first open space on a side adjacent the structure and opposite the second expanding tube assembly, the third housing having an first end in contact with the first housing; and a fourth housing coupled to the first portion on the second side, the fourth housing defining a second open space on a side adjacent the structure and opposite the first expanding tube assembly, the fourth housing having a second end in contact with the second housing.
 9. The frangible joint of claim 8 wherein the first end and second end are substantially co-planar with the fracture plane.
 10. The frangible joint of claim 8 wherein: the at least one notch includes a first V-shaped notch on the first side and a second V-shaped notch on the second side; the first wall has an edge adjacent the first V-shaped notch; and the second wall has an edge adjacent the second V-shaped notch.
 11. The frangible joint of claim 10 wherein: the first V-shaped notch has an open side contiguous with the first open space; and the second V-shaped notch has an open side contiguous with the second open space.
 12. The frangible joint of claim 11 wherein: the first end includes a first keyway that removably couples the first housing and the third housing; and the second end includes a second keyway that removably couples the second housing to the fourth housing.
 13. The frangible joint of claim 12 wherein the first housing is coupled to the fourth housing and the first portion by a plurality of first fasteners.
 14. The frangible joint of claim 13 wherein the second housing is found to the third housing and the second portion by a plurality of second fasteners.
 15. A method of separating portions of a structure, the method comprising: providing a structure having a first portion and an adjacent second portion with a notch disposed therebetween; providing a first housing coupled to the first portion and having a first slot adjacent the first portion; providing a second housing coupled to the second portion on a side of the structure opposite the first housing, the second housing having a second slot adjacent the second portion; providing a first expanding tube assembly having a first metallic tube containing a first explosive core disposed within a first elastomeric member; providing a second expanding tube assembly having a second metallic tube containing a second explosive core disposed within a second elastomeric member; detonating the first explosive core to expand the first metallic tube; and fracturing structure at the notch in response to the expansion of the first metallic tube.
 16. The method of claim 15 further comprising detonating the second explosive core and expanding the second metallic tube when the first explosive cord does not activate.
 17. The method of claim 16 wherein the first slot has a first wall adjacent the notch and the second slot has a second wall adjacent the notch.
 18. The method of claim 17 further comprising providing a first open space on a side of the first portion opposite the first expanding tube assembly, the first open space having an end defined by the second wall.
 19. The method of claim 18 further comprising deflecting a portion of the first portion into the first space when the first explosive core detonates.
 20. The method of claim 19 further comprising: providing a second open space on a side of the second portion opposite the second expanding tube assembly, the second open space having an end defined by the first wall; and deflecting a portion of the second portion into the second space when the second explosive core detonates. 